Conserving different spatio-temporal dimensions of biological
diversity may help maintain ecosystem functions such as primary
productivity under global change. The range of environmental
conditions that plant species occupy - their environmental niche
widths - approximate the degree of ecological specialisation in
a community, potentially influencing current primary productivity
(Fig. 1).
Preliminary models suggest the influence of community mean
niche width on primary productivity is greater than either rainfall or
temperature themselves. However, community mean leaf area
is a stronger influence on primary productivity than temperature
niche width. Communities with wider mean rainfall niches have
greater magnitude and lower variation of primary productivity.
Conversely, communities with narrower mean temperature niches
have greater primary productivity magnitude and lower variation.
Further modelling could incorporate the effects of spatial non-
stationarity and phylogenetic relationships between species on
ecosystem functions such as primary productivity.
We use structural equation models to test whether mean
community niche width influences the magnitude and variation of
community primary productivity in the Australian Wet Tropics,
above and beyond community mean traits values (e.g. leaf area)
and current environmental conditions.
Species niche width (NW, Fig. 2) is defined as the middle 90% of
rainfall (mm) and temperature (°C) values for all geographic
records of Wet Tropics tree species across Australia. Trees with
niches centred beyond the middle 90% of temperature values OR
the driest 5% of rainfall values for the Wet Tropics - based on their
geographic records - were excluded from analysis. Community
niche width is defined as the average niche width of all tree
species occurring at each of 492 Wet Tropics sites.
Fig. 1). Conceptual equation predicting wider community mean niche widths
drive lower magnitude and greater variation of community primary productivity.
Fig. 3). Scatterplots of primary productivity magnitude (average daily gross
primary productivity in grams of carbon from 01/2001-12/2012) and variation
(ratio of the standard deviation in primary productivity to the mean) for 492 Wet
tropics tree communities. Second order polynomial regression lines are plotted
in orange.
Fig. 4). Observed variable structural equation models, assuming all variables are
measured directly. Single headed arrows represent hypothesised causal paths.
Positive standardised path coefficients are in blue, negative in red and non-
significant paths are dashed (α = 0.05). Arrow width is proportional to strength of
path coefficients,.
Bioregional primary productivity
and community-level niche width
Future directions
Hugh Burley
1
, Karel Mokany
1
, Simon Ferrier
1
and Shawn Laffan
2
1
UNSW school of BEES, Sydney Australia.
2
CSIRO Land and Water, Canberra Australia.
Fig. 5). A). 100,00 continental geographic records for 745 trees from the Atlas
of Living Australia (http://www.ala.org.au/). B). 527 10m × 50m vascular plant
community surveys, with 745 trees recorded at the sites that were within the
Wet Tropics environmental extremes. Sites are overlain with interpolated 250m
surfaces (1976-2005) of annual rainfall (mm, blue) and maximum temperature
of the warmest period (°C, orange) C). Example vegetation communities of
north Queensland, Australia, near Cairns, top, and Mount Carbine, bottom.
Continental distribution of
Argyrodendron polyandrum;
rain niche width = 797 mm
temp niche width = 3.86 °C
Wet Tropics study region
B).
Tree richness in 20km cells
> 56
1
community mean rainfall
niche width =
mean(NW a, b, c)
high rainfalllow rainfall site i
species c).records
NW c
species b). records
NW b
species a). records
NW a
Fig. 2). Quantifying community mean rainfall niche width for a hypothetical site.
community
mean temp
niche width
R
2
= 0.020
community
mean
leaf area
R
2
= 0.666
temperature
community
GPP
magnitude
R
2
= 0.545
0.794
-0.141
-0.105
-0.186
-0.589
1.057
Rain (mm)
6945
542
527 community surveys
(745 tree species)
CAIRNS
MOUNT CARBINE
Temp (°C)
36.8
24.1
A).
ECOSYSTEM & BIODIVESRITY KNOIWLEDGE
LAND & WATER FLAGSHIP.
macroecologicalmodelling.com
.
CAIRNS
- Tall closed rainforest, annual rainfall ~2800 mm, max temp of
warmest period ~ 31.8 °C, tropical monsoonal climate
MOUNT CARBINE
- Eucalypt low open woodland, rainfall ~945 (mm), temp ~32.2°C,
Tropical wet-dry savannah climate
C).
community
mean temp
niche width
R
2
= 0.020
community
mean
leaf area
R
2
= 0.666
temperature
community
GPP
variation
R
2
= 0.254
0.794
-0.141
-0.105
-0.174
0.260
-0.618
community
mean rainfall
niche width
R
2
= 0.381
community
mean
leaf area
R
2
= 0.922
rainfall
community
GPP
variation
R
2
= 0.213
1.004
0.617
-0.073
-0.072
-0.297
-0.122
community
GPP
magnitude
variation σ
community
mean
environmental
niche width
community
mean
leaf area
environment
+
-
-
x
σ
-
x
community
mean rainfall
niche width
R
2
= 0.381
community
mean
leaf area
R
2
= 0.922
rainfall
community
GPP
magnitude
R
2
= 0.504
1.004
0.617
-0.073
0.243
0.734
-0.216
Structural equationsAim
Data sources
Niche width
Bivariate regressions
